The present invention relates generally to ion implantation devices, and, more particularly, to an ion beam uniformity and angular distribution measurement systems and methods.
Ion implantation is a physical process, as opposed to diffusion, which is a chemical process, that is employed in semiconductor device fabrication to selectively implant dopant into semiconductor and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and the semiconductor material. For ion implantation, dopant atoms/molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a wafer. The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface.
An ion implantation system is a collection of sophisticated subsystems, each performing a specific action on the dopant ions. Dopant elements, in gas or solid form, are positioned inside an ionization chamber and ionized by a suitable ionization process. In one exemplary process, the chamber is maintained at a low pressure (vacuum). A filament is located within the chamber and is heated to the point where electrons are created from the filament source. The negatively charged electrons are attracted to an oppositely charged anode also within the chamber. During the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a host of positively charged ions from the elements in the molecule.
Generally, other positive ions are created in addition to desired dopant ions. The desired dopant ions are selected from the ions by a process referred to as analyzing, mass analyzing, selection, or ion separation. Selection is accomplished utilizing a mass analyzer that creates a magnetic field through which ions from the ionization chamber travel. The ions leave the ionization chamber at relatively high speeds and are bent into an arc by the magnetic field. The radius of the arc is dictated by the mass of individual ions, speed, and the strength of the magnetic field. An exit of the analyzer permits only one species of ions, the desired dopant ions, to exit the mass analyzer.
An acceleration system, referred to as a linear accelerator, is employed in some instances to accelerate or decelerate the desired dopant ions to a predetermined momentum (e.g., mass of an dopant ion multiplied by its velocity) to penetrate the wafer surface. For acceleration, the system is generally of a linear design with annular powered electrodes and pairs of quadruple lenses along its axis. The quadruple lenses are powered by negative and positive electrical potentials. As the dopant ions enter therein, they are accelerated therethrough by the powered electrodes and are (as a beam) selectively focused and defocused by the quadruple lenses.
Continuing on, the dopant ions are directed towards a target wafer at an end station. The dopant ions, as a beam, impact the wafer with a specific beam current. In order to obtain a substantially uniform dose distribution at the target, the beam is required to be substantially uniform and an angle of incidence of the beam is also required to be substantially uniform. Accordingly, suitable systems and methods for measuring beam uniformity and angular distribution are desirable.
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention facilitates semiconductor device fabrication by monitoring uniformity of beam current and angle of incidence at various locations throughout an ion beam (e.g., a wider portion of a ribbon beam). One or more uniformity detectors are employed within an ion implantation system (e.g., single wafer based system and/or a multiple wafer based system). The detector(s) are operative to provide uniformity measurements before ion implantation (e.g., calibration), during ion implantation (e.g., in situ), and/or after ion implantation (e.g., verification). Based on the uniformity measurements, generation of an ion beam can be adjusted to improve uniformity as indicated. As a result, ion implantation can be performed with an improved uniformity and under tighter process controls.